The invention relates to a personal security system for locating emergency transmissions. More specifically the invention pertains to such systems including a portable communicator actuated in an emergency to send wireless signals that are used by a monitoring station to locate and display the location of the sending communicator.
Recently developed personal security systems locate subscribers in an emergency. The systems are installed in a protected region, such as a college or hospital campus, shopping center or building complex, and display the location of the emergency on a monitor at a central station.
A typical system is based on a portable transmitter carried by a subscriber and actuated in an emergency to send radio frequency signals identifying the transmitter to the system. Fixed receivers are installed at predetermined locations throughout the protected region. The receivers detect emergency transmissions and relay the transmitted information to the central monitoring station. The monitoring station identifies the subscriber to which the transmitter is assigned, locates the emergency based on the receivers that detect the transmission and displays the location to call appropriate security personnel. Examples of these and similar systems are disclosed in Shields U.S. Pat. No. 4,998,095, issued Mar. 5, 1991; DeMarco U.S. Pat. No. 4,764,757, issued Aug. 16, 1988; Levinson U.S. Pat. No. 4,611,198, issued Sep. 9, 1986 and Toner U.S. Pat. No. 5,365,217, issued Nov. 15, 1994.
Improved approaches for locating an emergency transmission are disclosed in Kostusiak et al. U.S. Pat. No. 5,115,224, issued May 19, 1992, and Malvaso et al. U.S. Pat. No. 5,416,466, issued May 16, 1995. In addition to the known positions of the detecting receivers, Kostusiak and Malvaso use relative signal strength between several receivers to more accurately locate the emergency transmission.
While existing approaches provide many advantages in personal security systems, they generally identify or display only a single location for each emergency. If a subscriber flees from an attacker, or is forced under duress to accompany the attacker, the system does not track the movement or display the path or direction of travel.
The present invention is directed to improvements in personal security systems and overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the invention, a portable communicator, for use with a personal security system, includes a transmitter for sending wireless signals identifying the communicator to the system. A manually operated actuator initiates the transmission, which is then repeated automatically over a predetermined time interval exceeding five minutes. The transmissions are discontinued at the end of the predetermined time interval or by operating the communicator in a second non-emergency mode such as a test. According to more specific features, the transmissions repeat at least once a minute for a predetermined time interval exceeding ten minutes. Still more specifically, the identifying signals are transmitted as a multi-packet signal stream repeated approximately once every thirty seconds for an interval of approximately fifteen minutes. The transmitter is dormant between transmissions.
According to other aspects of the invention, the identifying signals include a tracking bit that is set to a first state for the manually initiated transmission and a second state different from the first state for the automatic transmissions. The tracking bit permits differentiation at a monitoring station between the manually initiated and automatic transmissions.
Other aspects of the invention include a plurality of fixed receivers at predetermined locations in a protected region for detecting the emergency transmissions and a central monitoring station that locates the transmissions based on the fixed receivers detecting the transmissions. The monitoring station tracks and simultaneously displays multiple locations of successive transmissions. More specifically, the monitoring station compares the locations of first and second successive transmissions, a) displays both locations when they are spaced more than a predetermined distance, and b) displays only the first of the two locations when they are spaced less than the predetermined distance. The monitor represents the multiple locations as icons that vary in size based on relative transmission time and are stacked so that any overlapping icons representing more recent transmissions are on top.
These and other features and advantages of the invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.